Microwave Reflection Research Articles

Microwave absorption properties of (1 − x)La0.85Ag0.15MnO3/x graphene (x = 0, 3, and 5 wt.%) composites

AbstractComposite of (1 − x)La0.85Ag0.15MnO3/x graphene (x = 0, 3, and 5 wt.%) and epoxy resin with a ratio of 4:1 were prepared to investigate the influence of the addition of graphene in (1 − x)La0.85Ag0.15MnO3/x graphene on real and imaginary parts of permittivity, permeability, as well as microwave reflection loss (RL), using a vector network analyzer in the 8–18 GHz of the frequency range. It is found that the value of RL is smaller at x = 3 wt.% (−20.74 dB at 14.85 GHz) and 5 wt.% (−14.81 at 16.50 GHz) compared to at x = 0 wt.% (−8.89 dB at 15.90 GHz). The result indicates that microwave absorption properties significantly improved as a result of the addition of graphene. It is suggested that the addition of graphene enhanced the dielectric loss–related mechanism such as interfacial polarization and conduction loss resulting in an improvement of microwave absorption performance for both x = 3 wt.% and x = 5 wt.% samples. It also shows that the observed enhanced microwave absorption properties may also be influenced by the resistivity of the sample as x = 3 wt.% sample exhibits enhanced microwave absorption properties and the lowest resistivity among the studied samples.

Improved Microwave Ocean Emissivity and Reflectivity Models Derived from Two-Scale Roughness Theory

Improved Microwave Ocean Emissivity and Reflectivity Models Derived from Two-Scale Roughness Theory

Microwave Observations of Ganymede's Sub‐Surface Ice: I. Ice Temperature and Structure

AbstractOn 7 June 2021, Juno flew within 1,000 km of Ganymede's surface, partially mapping its ice shell at six frequencies ranging from 0.6 to 22 GHz. The radiance at these frequencies originates from successively deeper layers of the sub‐surface and may reach depths of 24 km at 0.6 GHz. The MWR observations cover a latitude range from 20°S to 60°N and a longitude range from 120°W to 60°E. We present brightness temperature and derived reflectivity maps of Ganymede with a spatial resolution of up to ∼140 km. The microwave brightness temperature at all MWR wavelengths is anti‐correlated with the visible brightness of the terrain. Normalizing the MWR brightness temperatures using a thermal model for the ice shell reveals that the brightest regions are significantly more reflective in the microwave than the dark regions and that all terrain types are more reflective than is expected from a solid ice surface. We suggest that multiple reflections of the colder sky background at sub‐surface interfaces (e.g., fractures) explain the depressed brightness temperatures observed in brighter terrain types. A thin silicate or salt contaminant surface layer, which is significantly more reflective than ice in the microwave, could explain the microwave reflectivity in the dark regions with little to no contribution from sub‐surface fractures. The observed 0.6–1.2 GHz brightness temperature difference suggests an upper bound on the ice shell conducting layer depth of 150 km in the observation area.

TriLoc: Toward Accurate Indoor Localization With Assistance of Microwave Reflections

With the development of the Internet of Things (IoT), indoor localization technology plays a vital role in smart factories, smart cities, and other fields. When using the network infrastructures such as Wi-Fi, some conventional localization technologies usually need multiple access points (APs), which involve time and data synchronizations. As a result, those drawbacks hinder the deployment of those localization technologies. In this article, we propose TriLoc, a single AP-based indoor localization system with the assistance of microwave reflections, which has the minimum overheads compared to the existing schemes. The insight is that the reflection paths and the direct path experience the same phase errors, and thus, it can be used for locating the user device using only a single AP. In the system, we first estimate the angle of arrivals (AoA) and time of flight (ToF) of propagation paths and then use the multipath triangle that consists of one first-order reflection path and the direct path to locate the user device. Finally, we construct the prototype using software-defined radio and evaluate it in various indoor environments. The experimental results show that TriLoc can achieve submeter localization accuracy using only a single AP.

Electromagnetic absorption enhancement of concrete using metamaterials

Electromagnetic wave (EMW) pollution adversely affects information, facilities safety, and human health, leading to the development of EMW absorbing materials, especially absorbing concrete. Here, the influence of arrangement ways of concrete iron on microwave reflectivity was analyzed, and a split ring resonator (SRR) was designed and introduced to steel-reinforced concrete to improve the EMW absorbing performance of the concrete. The simulation results show that by tuning the diameter and arrangement ways of concrete iron and introducing SRR structure, an EMW absorption concrete which can display 0.3% reflection loss ([Formula: see text]% absorption) at 2.34[Formula: see text]GHz was designed and realized. The reflectivity of concrete iron and EMW absorption capacity of concrete were investigated by a vector network analyzer, and the experimental results almost agree with the simulation results. The reflection and absorption of EMW are caused by magnetic resonance and conductive loss, magnetic loss, respectively.

Calibrated transmission and reflection from a multi-qubit microwave package.

We report calibrated microwave transmission and reflection measurements of a qubit sample holder at millikelvin temperatures. The methodology we present extends our previous work on one-port cryogenic short-open-load (SOL) calibration to a two-port SOLT measurement by implementing an unknown thru (T) standard. We report the resulting calibrated transmission and reflection at millikelvin temperatures through a printed circuit board that is installed into the sample holder. Finally, we consider a cascade of components at the end of a qubit drive line that includes (1) a cryogenic attenuator, (2) a coaxial cable, and (3) a qubit sample holder. Using experimentally determined parameters for return losses for all three components, we calculate the negligible state-preparation error in the frequency band of 5-7GHz due to control pulse distortions arising from reflection at the coaxial launches. Taken together, our results highlight the utility of calibrated cryogenic scattering parameter measurements for the validation of qubit packaging and the wiring in its immediate vicinity.

Microwave polarization conversion and reflection loss mechanism of complementary-modeled Rossler-based chaotic metamaterial

The complementary-modeled Rossler chaotic metamaterial (CRCM) with FR-4 dielectric layer is proposed to design metamaterial absorber with multi-resonance peaks. Under “master-slave” boundary condition in high-frequency structure simulator (HFSS) software, the electric field between adjacent boundaries presents phase difference which can simulate an infinite array. The research results show that the CRCM demonstrates multi-resonant peaks from 4 GHz to 10 GHz, and the area of metal patterned-layer can obviously regulate the resonant peaks. The CRCM presents a linear polarization conversion peak around 5.80 GHz, its polarization conversion ratio (PCR) is near 100%. The PCR is also larger than 80% from 5.56 GHz to 5.95 GHz. Through the surface current density distribution and the comparison between the CRCM and complementary-modeled double ring metamaterial (CDRM), the main factors generating polarization conversion are the asymmetry of metal pattern layer and magnetic resonance caused by reverse current. The CRCM also has two strong absorption peaks located at 6.31 and 9.37 GHz, respectively. Dielectric loss and ohmic loss are the main microwave loss mechanisms proved by volume and surface power loss density distribution. The resonant frequencies derived from [Formula: see text] resonant circuit are well consistent with the simulation data and measurement results.

A comparison between microwave reflection loss of MIL-53 derived Fe2O3 and MOF-71-derived Co3O4 through direct and indirect heat treatment

In this study, the metal oxide derived from Co-based MOF-71 and Fe-based MIL-53 with two different solid-state thermolysis procedures: an indirect thermal treatment of –OH treated MOFs and direct thermolysis of the MOFs were synthesized and their microwave absorption properties were investigated. The X-ray diffraction patterns of the samples were recorded to confirm the successful synthesis of the MOFs and the thermolysis products. Field emission scanning electron microscopy (FE-SEM) images illustrated nanocomposites' morphology and uniform structure. Synthesized MOFs were represented the morphology of nano-scale particles, which would dramatically impact their specific surface area, as confirmed by the BET results. The adsorbents' complex permeability and permittivity parameters were investigated in 8–12 GHz range. The maximum reflection loss (RL) was − 37.01 dB at 9.22 GHz for the indirect Co3O4 and −35.03 dB at 9.99 GHz for the indirect Fe2O3.

Detection of Void and Crack Defects in Type IV Hydrogen Storage Vessels by Microwave Technique

Non-destructive testing based on microwave technique has been developing rapidly. In the present study, microwave-based method was used to detect void and crack defects in the carbon fiber composite wound layer of type IV hydrogen storage vessels. Taking advantage of a vector network analyzer, the reflection coefficient S11 of type IV hydrogen storage vessel samples without defects and with a void or a crack defect in the composite wound layer was measured. The defect-containing vessels exhibited S11 values much different from those of vessels without defects, according to which the defects can be detected. Additionally, identification of the two defects can be realized by analyzing the S11 values, as the void gives rise to more reflection of microwave than the crack. During the inspection, only when the horn antenna is against the defect does the S11 show significant changes, suggesting the detection sensitivity of the method. This study lays a solid foundation for the development of microwave inspection of defects in the composite wound layer of type IV hydrogen storage vessels.

Identifying Void and Crack Defects in Type III Hydrogen Storage Vessels Based on Microwave Inspection

Microwave technique has become a promising candidate for non-destructive testing. In this study, microwave-based method was used to inspect type III hydrogen storage vessels and to identify void and crack defects in the carbon fiber composite wound layer. Using a vector network analyzer, the reflection coefficient S11 of type III hydrogen storage vessel samples with no defects and with a void or a crack defect in the composite wound layer was measured. The defect-containing vessels had S11 values significantly different from those of vessels without defects, based on which the defects can be detected. Moreover, identification of the two defects can be achieved by comparing the values of S11, as the void results in more microwave reflection than the crack. During the inspection, only when the horn antenna is against the defect does the S11 show great changes, indicating the detection sensitivity of the method. This work provides new insights into inspection of defects in the of carbon fiber composite wound layer of type III hydrogen storage vessels.

In Situ Measurement of Absorbing Properties of Materials Based on Near-Field Reflection Method

To meet the requirements of the in-situ measurement of the absorbing properties of materials and break through the limitations of the transmission line probe method in ultra-wideband and high-precision measurement, this paper presents in-situ measurement technology for the absorbing properties of materials based on near-field reflection testing. A miniaturized ultra-wideband antenna, a decoupling structure and a shielding cover are designed, and an in-situ measurement probe is constructed. By integrating the probe with a microwave transceiver module as well as a control processing module, a handheld broadband microwave reflectivity test instrument is developed and its performance is verified. The measurement accuracy of the proposed instrument is higher than that of transmission line probes, the deviation of its test results from those of standard arch systems is less than 1.5 dB in the reflectivity range of 0 to -20 dB; its test frequency band is wider, and its frequency band covers 2-18 GHz. The instrument is suitable for accurately measuring the absorbing properties of materials with thicknesses of less than 1.5 mm.

An X-band compact rectangular waveguide TE10-circular waveguide TE01 mode converter

This paper proposed an X-band compact efficient rectangular waveguide TE10-circular waveguide TE01 mode converter and conducted its structure design, theoretical analysis, numerical simulation, and experimental research. This mode converter is composed of a rectangular waveguide TE10–TE20 mode converter and a rectangular waveguide TE20-circular waveguide TE01 mode converter. In the design of the rectangular waveguide TE20-circular waveguide TE01 mode converter, a rectangular waveguide step is used to counteract the microwave reflection due to the discontinuity of the rectangular–circular waveguide connection, and two choke slots are involved to suppress the TE21 mode in the circular waveguide by cutting off the axial component of its surface current on the waveguide wall, so as to improve the TE01 mode conversion efficiency. The simulation results show that the reflection coefficient of the mode converter is less than 5% and the TE01 mode conversion efficiency is about 98.4% at the operation frequency of 9.3 GHz. The bandwidth with a transmission coefficient greater than 98% is about 200 MHz. The back-to-back experimental system is demonstrated, and the experimental results show that the measured TE01 mode conversion efficiency is about 98.2%, which is consistent with the simulation result.

Lead-acid batteries (LABs) and the thermogravimetric analysis of Pb metal reduction from PbO2 via microwave heating at 2.45 GHz

The lead (Pb) in lead-acid batteries (LABs) accounts for up to 60% of their total weight and 80% of the metallic Pb produced worldwide. As a toxic substance but sought-after resource, developing a method to reclaim Pb from spent batteries, both safely and efficiently, is highly desirable. To this end, this paper explores the application of microwave heating to reduce Pb from PbO2, a component of LAB pastes, using a carbon (C) reductant. Various experiments were conducted between 200 and 1000 W to determine mass loss kinetics using a homemade thermogravimetric apparatus. The mechanisms and kinetics of the reactions, and their resultant phases, are discussed in comparison to differential thermal analyses (TG-DTA) of the same samples. Microwave heating was found to be highly effective, resulting in up to a 97% recovery of Pb metal at < 300 °C; however, complete reduction was unrealized due to crucible interference, microwave penetration depth, and the reflection of microwaves as Pb metal formed. The reduction and decomposition reactions were evaluated using X-ray diffraction (XRD).

Simulating the effects of fabrication tolerance on the performance of Josephson travelling wave parametric amplifiers

We present the simulated performance of a Josephson traveling wave parametric amplifier based on a one-dimensional array of radio-frequency single-junction superconducting quantum interference devices. Using the capabilities allowed by the WRspice simulation platform and previous works on this scheme, we include in our study the effects of fabrication tolerances in the device parameters on the gain of the amplifier. Our simulations show the negative effects of parameter variation and the resulting microwave reflections of signal and pump waves between individual cells. We present a method to understand the inner dynamics of the device using an impedance model that substitutes the need to simultaneously consider phase bias points and wave mixing dynamics. This should allow the application of the results presented here to more complex schemes, which promise higher amplification and fewer drawbacks. We highlight the strict limitations on parameter spread in these devices while also discussing the robustness of the scheme to defects.

Assessment of surface recombination in mid-wave infrared InAsSb nBn detectors using transient microwave reflectance

Investigation of surface recombination is an important area for infrared detectors as the demand for smaller pixels increases. In this study, we use transient microwave reflectance to characterize the minority carrier lifetime of InAsSb nBn structures under three conditions: As-Grown, blanket Barrier-Etched, and SU-8 Passivated blanket barrier-etched. A qualitative comparison of these three samples shows that the minority carrier lifetime decreases for the Barrier-Etched sample compared to the As-Grown sample, indicating that the minority carrier lifetime is sensitive to changes in the sample surface, specifically the introduction of surface states. We compare these samples quantitatively using a polynomial fit (A−1 + Bn + Cn2). We find for the As-Grown sample A = 1.22 ± 0.45 µs, B = 2.5 ± 0.2 × 10−12 cm3/s, and C = 5.004 ± 4.996 × 10−31 cm6/s, for the Barrier-Etched sample A = 1.17 ± 0.40 µs, B = 9.9 ± 0.2 × 10−12 cm3/s, and C = 9.502 ± 9.498 × 10−30 cm6/s, and for the Passivated sample A = 1.34 ± 0.45 µs, B = 5.3 ± 0.5 × 10−12 cm3/s, and C = 5.500 ± 4.500 × 10−33 cm6/s.

Electrochemically modulated interaction of MXenes with microwaves.

Dynamic control of electromagnetic wave jamming is a notable technological challenge for protecting electronic devices working at gigahertz frequencies. Foam materials can adjust the reflection and absorption of microwaves, enabling a tunable electromagnetic interference shielding capability, but their thickness of several millimetres hinders their application in integrated electronics. Here we show a method for modulating the reflection and absorption of incident electromagnetic waves using various submicrometre-thick MXene thin films. The reversible tunability of electromagnetic interference shielding effectiveness is realized by electrochemically driven ion intercalation and de-intercalation; this results in charge transfer efficiency with different electrolytes, accompanied by expansion and shrinkage of the MXene layer spacing. We finally demonstrate an irreversible electromagnetic interference shielding alertor through electrochemical oxidation of MXene films. In contrast with static electromagnetic interference shielding, our method offers opportunities to achieve active modulation that can adapt to demanding environments.

Tunable Head-Conducting Microwave-Absorbing Multifunctional Composites with Excellent Microwave Absorption, Thermal Conductivity and Mechanical Properties

Developing composite materials with both thermal conductivity and microwave absorption is an effective strategy to solve the problems of heat dissipation burden and microwave radiation interference caused by the development of miniaturization and high performance of portable electronic equipment. However, these properties are not easy to simultaneously implement due to the limitation of single type fillers with a single particle size, inspiring the possibility of realizing multifunctional composites with the introduction of composite fillers. In this work, using alumina (Al2O3) and zinc oxide (ZnO) as head-conducting fillers, carbonyl iron (Fe(CO)5) as microwave-absorbing fillers, silicone rubber (SR) composites (Al2O3/ZnO/Fe(CO)5/SR) with enhanced microwave absorption, high thermal conductivity and good mechanical properties were successfully mass prepared. It was found that the composites can achieve a thermal conductivity of 3.61 W·m−1·K−1, an effective microwave absorption bandwidth of 10.86–15.47 GHz. Especially, there is an effective microwave absorption efficiency of 99% at 12.46–14.27 GHz, which can realize the integration of electromagnetic shielding and heat dissipation. The compact microstructure, formed by the overlapping of large particle size fillers and the filling of their gaps by small particle size fillers, is helpful to enhance the thermal conduction path and weaken the microwave reflection. The heat-conducting microwave-absorbing Al2O3/ZnO/Fe(CO)5/SR composites also have the advantages of thermal stability, lightness and flexibility, providing a certain experimental basis for the research and development of high-performance and diversified composites.

Uncertainties Caused by Noise for Microwave Interferometric and Reflection Measurements of Extreme Reflection Coefficients

This article concerns an uncertainty analysis of interferometric transmission measurements and standard reflection measurements of extreme impedances (extreme reflection coefficients) and broadens the scope of previously published works. Specifically, the paper focuses on revealing fundamental limits influencing achievable measurement accuracy and precision by means of the law of uncertainty propagation. The analysis considers sources of uncertainty influencing every measurement, in particular phase noise and thermal noise. The proportion of uncertainties of standard reflection measurements and interferometric measurements are derived theoretically and experimentally verified for two cases with dominant either the phase noise or the thermal noise. The values determined experimentally in a frequency band from 2 GHz to 4.5 GHz agree well with the values derived theoretically.

MODELLING MICROWAVES IN BAUXITE

AbstractSending microwaves through bauxite ore allows almost continuous measurement of moisture content during offload by conveyor belt from a ship. Data and results from a microwave analyser were brought to a European Study Group with Industry at the University of Limerick, with the over-arching question of whether the results are accurate enough. The analyser equipment uses linear regression against phase shifts and signal attenuation to infer moisture content in real time. Simple initial modelling conducted during the Study Group supports this use of linear regression for phase shift data. However, that work also revealed striking and puzzling differences between model and attenuation data.We present an improved model that allows for multiple reflections of travelling microwaves within the bauxite and in the air above it. Our new model uses four differential equations to describe how electric fields change with distance in each of four layers. By solving these equations and taking reflections into account, we can accurately predict what the receiving antenna will pick up.Our new solution provides much-improved matches to data from the microwave analyser, and indicates the deleterious effects of reflections. Modelled signal strength behaviour features a highly undesirable noninvertible dependence on bauxite mixture permittivity.Practical measures that might be expected to reduce the effects of microwave reflections and improve the accuracy of microwave analyser results are suggested based on our improved model solution. This modelling approach and these results are anticipated to extend to the analysis of moisture content during transport on conveyor belts of other ores, slurries, coal, grains and pharmaceutical powders, especially when the depth of the conveyed material is variable.

A New Algorithm for Measuring Vegetation Growth Using GNSS Interferometric Reflectometry

The use of global navigation satellite system interferometric reflectometry (GNSS-IR) to measure vegetation growth status has become a rapidly growing technique in remote sensing. GNSS signals reflected by the soil surface affect the accuracy of vegetation growth status (vegetation cover density) measurement, and the influence of soil moisture (SM) varies. This study establishes a calibration model that can reduce the influence of SM and snow layer on reflectivity. We used a direct-reflected signal amplitude ratio and GNSS-IR altimeter based on the Lomb–Scargle Periodogram to calculate the reflectivity of vegetation and snow layer depth. GNSS data from plate boundary observation were used to verify the validity of our model. The results show that reflectivity correlates better with vegetation growth status after calibrating the influence of the SM and snow layer. Moreover, the correlation increased by nearly 0.14. This study analyzed the influence of the snow layer and found that it had a noticeable effect on vegetation growth status measurement when the snow depth was over 30 cm. Furthermore, a fusion method is proposed to improve the accuracy of vegetation growth status measurement by combining the reflectivity and normalized microwave reflection index (NMRI). The experimental results show that better performance can be obtained compared to the single observation of the reflectivity and NMRI, and the best correlation between the measured and in situ normalized difference vegetation index is over 0.91, and the root mean square error decreases to 0.1893.